Sorting/storage device for wafers and method for handling thereof

ABSTRACT

Sorting/storage device for wafers. A sorting device is provided in which at least two cassettes containing wafers may be present and the wafers are moved from one cassette to the other cassette or vice versa. If appropriate, a measuring station may be present in the sorting device. In the immediate vicinity of the sorting device, the cassettes are stored in a magazine which is designed for this purpose and the cassettes are moved using a handling device for cassettes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for sorting wafers.

2. Description of the Related Art

Such a sort device is generally known in the prior art. If wafers arebeing treated batchwise, it is customary to include test wafers in abatch as well as end wafers wherein because they are used as “fill” inthe batch, the quality of treatment of these wafers is lower due to theposition in the treatment device, and these wafers cannot be usedfurther, or can only be used further after they have been treated. If abatch of wafers comprises, for example, 100 wafers, they are fed in anumber of cassettes to the appropriate treatment device, such as afurnace. Normally, such cassettes contain approximately twenty-fivewafers, so that in such a case approximately four wafer cassettes arefed to the furnace. A number of these cassettes are filled only with“product” wafers. Moreover, a number of cassettes contain test wafersand the end wafers described above.

In addition to the sorting device, there are normally a separate storagedevice for cassettes and one or more separate measuring stations forcarrying out measurements. This means that in the prior art three ormore separate housings are present, each separately provided with a(wafer- or cassette-)handling device and a particle-free environment.

The wafers are handled in the sorting device and in the measuringstations in a particularly particle-free environment. Higher demands areplaced on this environment than on a clean room in which wafers aretransported in closed pods. From the moment at which the transport podis opened and the cassette containing wafers is removed therefrom untilthe moment at which the cassette containing wafers is placed back in thetransport pod and the transport pod is closed, this particularlyparticle-free environment has to be maintained. By providing the podaround the wafer cassette with a standardized door (SMIF, FOUP) andplacing the cassette with this door against a wall of the sorting devicewith a closable opening and simultaneously opening cassette door andwall opening, it is possible to achieve a highly effective separationbetween clean room and wafer-sorting chamber. As a result, the demandswhich are imposed on the clean room can be of a low level, with acorresponding saving in the costs, while in the limited volume of thesorting device itself it is possible to maintain an environment whichsatisfies the most stringent of materials requirements. It is alsopossible to provide the environment of the sorting device with an inertgas, such as nitrogen. The same applies to the measuring station. Theretoo, the wafers are handled in a particularly particle-free environment.Each sorting station and each measuring station must be provided with alock mechanism. The storage of wafers in the closed cassettes can takeplace under less stringent clean-room conditions.

U.S. Pat. No. 4,776,744, from which the preamble of claim 1 is known,discloses a device for sorting wafers. A turn-table is present, havingseveral blades on which an indexer is provided for holding and movingtwo cassettes. The blades can be moved below a wafer gripper for removaland introduction of wafers out and in the cassettes.

SUMMARY OF THE INVENTION

The object of the present invention is to provide asorting/storage/measuring device which is easier and less expensive toproduce and in which the surface area required for the device can belimited without, reducing the throughout capacity. In addition, theflexibility is to be enhanced. In one embodiment, the device for sortingwafers stored in cassettes includes, among others, a housing, a waferhandling device arranged in a chamber to be sealed off with respect tothe housing, a part for receiving cassettes arranged in the housing andseparated from the chamber by a partition, a store for closablecassettes arranged in the housing, and a handling device for closablecassettes arranged in the housing.

As a result, the sorting options are considerably increased, due to thefact that all the cassettes in the storage device are available to thesorting device. In addition, the necessary measurements can also becarried out during sorting without the need for transportation to aseparate measuring station. Consequently, the number of handlingoperations decreases and the capacity of the device can be increasedwhile reducing the surface area required. If the wafers are supplied andstored in cassettes in pods provided with a standard door (SMIF, FOUP),fewer lock mechanisms are required than with the three or more separatehousings according to the prior art. If certain types of wafer arealways present in a specific cassette, it is possible, by changingcassettes of this nature into a different cassette which is present inthe sorting device, to assemble a batch as desired. Naturally, it isalso possible to arrange different types of wafers in a storagecassette, so that exchange in the sorting device is less frequent.

It is possible for the sorting device to deal with more than twocassettes at a time.

According to an advantageous embodiment of the invention, the chamber inwhich the sorting is carried out comprises a measuring station or ameasuring station is arranged in functional relationship with the waferhandling device. Preferably this measuring station is provided in thespace wherein sorting is realised or a measuring station is providedadjacent thereto. Such a measuring station may, for example, be designedto test layer thickness of the treated wafers, to measure amount ofundesirable foreign particles which are present on/in the wafers and thelike.

The cassette-handling device is able to move the cassettes from theinsertion position to the store or to a turntable. The turntable movesthe cassette into the correct position for the lock mechanism via whichthe cassette is placed in active connection with the wafer-handlingrobot.

The store for cassettes may comprise any structure which is known in theprior art, such as a rotatable magazine.

The invention also relates to a method for assembling a (part of a)batch of wafers which is to be fed to a treatment device for wafers,comprising placing at least two cassettes containing wafers in activeconnection with a wafer-handling device and using the saidwafer-handling device to carry out a sorting operation by moving wafersfrom one cassette to the other and vice versa. According to theinvention, this method is characterized in that at least one of the saidcassettes is from a cassette store, the said cassettes being moved fromthe said store to the sorting station in a housing.

According to an advantageous embodiment of this method, the wafer issubjected to a measurement during the sorting operation. “During” isalso understood to encompass immediately before or immediately after thesorting operation.

The invention will be explained in more detail below with reference to astructure according to the prior art and an exemplary embodimentaccording to the invention. In the drawing:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a–c very diagrammatically show a number of devices according tothe prior art;

FIG. 2 shows a diagrammatic, perspective view of a sorting/storagedevice according to the invention; and

FIG. 3 shows a plan view of the various parts of this device accordingto the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 a, 40 denotes a sorting device which comprises a part(depicted highly diagrammatically) in which the cassettes 12 and 13 arearranged and a device for handling wafers which is denoted by a circle41. Using this device, wafers, for example, are removed from cassette 12and placed in cassette 13 in any desired order.

FIG. 1 b shows a storage device 42. A store is denoted by 43 and acassette-handling robot is denoted by 45. Using cassette-handling robot,cassettes 12, 13 are moved from the insertion position into store 43.

FIG. 1 c shows a measuring station 44 with a diagrammatically depictedmeasuring cell 45. Wafers from the cassette 12 are subjected to aspecific measurement in measuring cell 16.

To carry out a treatment in, for example, a furnace, such as adeposition process on a wafer, firstly, if required, measurements arecarried out on test wafers in one or more measuring stations 44, forexample the number of dust particles present before the treatment ismeasured. Then, a batch is assembled in device 40. Cassettes 12containing different wafers which are required for his purpose come fromstore 42. After the appropriate treatment has been carried out, thewafers are sorted again in station 40 and are stored in station 42. Thetest wafers are measured in one or more measuring stations 44.

Transport between the various stations takes place in the cassettes 12,13 and is taken care of by various operators or by acassette-transporting system.

FIGS. 2 and 3 show the single device according to the present inventionwhich combines the above devices and considerably simplifies thecomplicated operations while allowing more efficient handling of thewafers on a much smaller surface area.

In these FIGS. 2, 3, a sorting/storage device according to the presentinvention is denoted by 1. This device is arranged in a housing 2. Thishousing 2 is preferably itself placed in a chamber which is not shown,such as a clean room.

As can be seen from FIGS. 2 and 3, the housing is provided with apartition 4. Partition 4 provides a separation between chamber 23 andchamber 22. A cassette-handling device 25 such as a robot, and amagazine 8 for cassettes are situated in chamber 23. Communication withchamber 22 is realized via closable opening 37 which is designed in sucha manner that, when cassette 18 is placed against it, both this cassetteand the said opening 37 are opened. Consequently, it is possible for thewafer-handling device or wafer robot 24 arranged in chamber 22 tocollect wafers from the cassette in question or to position themtherein. This wafer-handling robot 24 is able to move both in thehorizontal plane and in the vertical plane and is controlled by controlunit 20. Any desired gas atmosphere can be maintained within a chamber22, for example a pure nitrogen atmosphere, in order to avoid any actionon the wafers, and the number of particles can be reduced still further.

Moreover, one or more measuring stations are situated adjacent tochamber 22. Each measuring station is able to determine one or moredifferent parameters, such as the layer thickness of material which hasbeen deposited on the wafer, the chemical and/or physical state of thismaterial, the number of dust particles on the wafer and the like. As canbe seen from FIG. 3, measuring stations may be placed in activeconnection with the wafer-handling robot at a number of positions.Moreover, it can be seen from FIG. 2 that if the height of the measuringstations is limited, two or more measuring stations can be placed aboveone another within the reach of the wafer-handling robot.

These cassettes 18 are arranged on a turntable 30. Usingcassette-handling device 25, cassettes can be moved from this turntable30 to store 8. This cassette-handling robot 25 comprises a jointed arm31 and a height-adjustment mechanism 35. Store 8 comprises a rotatable,cylindrical magazine provided with receptacles 26, at different levels27, which receive cassettes 17. Cassettes 12, 13, 17 and 18 are, ofcourse, identical. Store 8 is of rotatable design. As a result, andbecause the cassette robot 25 is vertically adjustable, any cassette canbe moved from the store onto the turntable 30 which is designed with tworecesses. It will be understood that table 30 may have a greater numberof levels.

On entry, the cassettes 12 and 13 are moved into the insertion/removalposition 33. As diagrammatically indicated in FIG. 3, it is possible,from this position, for example to place cassette 13 in store 8 or totransfer it directly to turntable 30.

When using so-called FOUPs, i.e. cassettes which normally close offtheir contents and are opened only on contact with partition 4, chamber23 may have the same atmosphere as the surroundings, for exampleclean-room conditions, and does not have to satisfy the higher demandsimposed when sorting the wafers for particle concentration and the like.

The device described above functions as follows. If, for example,cassette 13 which is empty is to be provided with a specific sequence ofdifferent types of wafers for treatment in, for example, a furnace, itis placed on turntable 30 using cassette-handling robot 25. Followingrotation of turntable 30, cassette 13 is situated in the position ofcassette 18. It is then opened. Before this, after this orsimultaneously, it is ensured that a cassette containing at least onedesired wafer is situated at a different level of turntable 30. For thispurpose, the top part of turntable 30 can move independently from bottompart of turntable 30. Rotation of turntable 30, like the movement of thesorting device 24, store 8 and cassette-handling device 25, iscontrolled by control unit 20. Then, the desired wafer is placed incassette 18 with the aid of wafer-handling device 24. If other wafersare required and are not present in the stock cassette used, this stockcassette is exchanged for another which may come from store 8. In thisway, a desired batch is assembled in cassette 18 and is removed againusing cassette-handling device 25.

After the treatment has finished, the cassette in question can be placedback on turntable 30 via handling device 25 and a wafer can be fed toeither the top or the bottom measuring station 16 with the aid ofwafer-handling device 24. In addition to a measuring station, there mayalso be a station for reading the wafer identification code and one forthe wafer orientation. Various types of measurements on various types oftest wafers or various types of measurements on the same test wafer arepossible.

The present invention considerably limits the logistics of the testwafers, since they no longer have to move along the various measuringstations and the storage/sorting device is multifunctional. In additionto advantages in the area of the housing and the atmosphere presenttherein, it is also possible to simplify automation, since the number ofwafer-/cassette-handling robots can be limited, as can their expensivecontrol unit 20.

Although the invention is described above with reference to a preferredembodiment, it will be understood that numerous amendments can be madeto this without departing from the scope of the present claims. Forexample, it is possible for the storage device to be designed in anyother way which is known from the prior art. Moreover, there may bedevices for determining the position of the wafer on the wafer-handlingrobot.

1. A device for sorting wafers stored in cassettes comprising: ahousing; a wafer handling device arranged in a chamber configured to besealed off with respect to the housing, wherein the wafer-handlingdevice accesses a measuring station configured to carry out measurementsdirectly on said wafers; a part for receiving at least two closablecassettes arranged in the housing and separated from said chamber by apartition, said part configured to independently position each receivedcassette against a related closable opening in said partition, whereinthrough opening of said closable opening said closable cassette isopened when placed against the opening and placed in communication withsaid chamber so that said wafer handling device can sort wafers bymoving the wafers into and out from one cassette and into an othercassette after opening each of said at least two cassettes; a store forclosable cassettes arranged in the housing; and a handling device forclosable cassettes arranged in the housing, wherein the store forclosable cassettes and the handling device for closable cassettes areseparated from the part for receiving at least two cassettes, whereinthe part for receiving at least two cassettes comprises a turntable,wherein said turntable comprises two or more levels which areindependently rotatable, wherein the turntable is configured to receiveone of the at least two cassettes on each of the two or more levels,wherein said turntable is configured to place each of the at least twocassettes in a position against a related closeable opening.
 2. Thedevice of claim 1, wherein the device is configured for sorting wafersstored in FOUPs.
 3. The device of claim 1, wherein the store forcassettes comprises a rotatable magazine.
 4. A method for assembling abatch of wafers in cassettes comprising the steps of: placing at least afirst and a second closed cassette in a store; employing a cassettehandling device to select and move a first cassette from the store to afirst closable opening in a sealed chamber; opening said first closableopening together with said first cassette; employing a cassette handlingdevice to select and move a second cassette from the store to a secondclosable opening in said sealed chamber; opening said second closableopening together with said second cassette; performing a directmeasurement of said wafers in a measuring station; and employing awafer-handling device, provided in said sealed chamber, to transferwafers to and from the measuring station communicating with said sealedchamber and to sort the wafers by transferring wafers directly betweenthe first cassette and the second cassette, wherein employing thecassette handling device to select and move the first cassettecomprises: moving the first cassette from the store to a recess on afirst level of a turntable; and rotating the first level of theturntable so as to move the first cassette to the first closableopening; and wherein employing the cassette handling device to selectand move the second cassette comprises: moving the second cassette fromthe store to a recess on a second level of the turntable; and rotatingthe second level of the turntable independently of the first level so asto move the second cassette to the second closable opening.
 5. Themethod of claim 4, further comprising the step of testing the wafersduring sorting the wafers.